The present invention relates to a primary part of a linear electrical machine, and to a linear electrical machine with a primary part.
Nothing in the following discussion of the state of the art is to be construed as an admission of prior art.
Linear electrical machines have a primary part and a secondary part which are arranged in opposite relationship and separated from one another by an air gap. The primary part is intended for electric current to be passed through it. It is possible for both the primary part and the secondary part to have active means for production of magnetic fields. For example, the primary part has a winding through which current can be passed, and the secondary part has permanent magnets. In addition, it is also possible for the primary part to have a plurality of active means for production of magnetic fields, and for the secondary part to be free of such means.
German patent document DE 10 2004 045 992 A1 discloses an electrical machine with a primary part which has all the magnetic sources of the electrical machine. The primary part has, for example, a winding through which current can be passed and permanent magnets whereas the secondary part is, for example, only in the form of a toothed iron reaction rail.
Unlike electrical machines which operate by rotation, linear electrical machines have end areas in which the electromagnetic part of the machine ends. If, for example, a linear motor is designed using a short stator construction, i.e. a primary part is sized shorter than a secondary part, the primary part has two end areas which are located in the influence area of the secondary part. The ends of the primary part interact with the secondary part such that it has a significant influence on the active force ripple and the passive force ripple, also referred to as the cogging force. Parasitic cogging forces which occur as a result of the magnetic interaction between the primary part and the secondary part are referred to as passive force ripple. This results in vibration, rough running and drag errors during machining processes.
Furthermore, the induced voltages, i.e. the electromotive forces (EMF), in the initial and end coils at the end faces of the primary part are generally less pronounced than in the central coils in view of an absent magnetic return path. As a consequence, the electrical machine does not have a symmetrical induced voltage and an additional current-dependent force ripple, which is referred to as active force ripple is experienced in addition to reductions in the force.
German patent document DE 10 2005 004380 A1 discloses a linear motor with force ripple compensation by using a force ripple compensation tooth of a predefined width, which is separated by an additional air gap from the normal air gap and is at a different distance from the adjacent teeth of the laminated core as the remaining teeth of the laminated core.
It would therefore be desirable and advantageous to address prior art shortcomings.